Mineral oil tests for the MiniBooNE detector

The MiniBooNE experiment will unambiguously confirm or refute the existence of the neutrino oscillation signal seen by the liquid scintillator neutrino detector (LSND) experiment at Los Alamos National Laboratory. MiniBooNE will search for the appearance of electron neutrinos in a beam of muon neutrinos. The MiniBooNE detector is a 12-m-diameter sphere filled with mineral oil and instrumented with photomultiplier tubes. The properties of the mineral oil chosen to fill this Cerenkov detector will be important to the experiment. The production of scintillation light in the oil, the attenuation of light across the detector, and the index of refraction of the oil are all important properties that must be known in order to properly model the detector. Fluorescence of the oil, optical dispersion, and oil density are also important quantities. The fluorescence spectra for several pure mineral oils as well as mineral oils doped with a small amount of various fluors were measured to determine the expected scintillation spectra from those oils. Index of refraction measurements were made in order to determine the Cerenkov angle and the dispersion for each oil. Attenuation tests were performed to rind an oil with maximal attenuation length and with no abnormal absorption features. This paper presents measurements of some of the oil properties, which are made at Fermilab using several experimental setups. Based on the results of these tests (and a price within budget constraints), Marcol 7 oil was selected for the MiniBooNE experiment.